Method of manufacturing metallic filamentary material



at ented @ct. l2, i926.

WILLIAM B. GER/O, OIE EAST ORANGE, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN MENTS, TO VTESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

METHOD OF MANUFACTURING METALLIC FILAMENTARY MATERIAL.

N0 Drawing.

My invention relates to the manufacture of metallic materials adapted to be sub .material, such as tungsten and similar highly refractory metals, unless specially treated will tend to alter internally when raised to a oint of incandescence in a lamp, and that the degree of alteration will depend upon such factors as the size of filament, efliciency at which it is operated, length of service, etc. One such formof alteration is manifested in what is coinmonly known as sagging, which is particularly noticeable in filaments of the coiled type or in lamps which are designed to be burned horizontally. The effect of sagging in a coiled filament results in adjacent turns of the wire comprising the helix either being separated or short circuited, and, in the case of a lamp having an uncoiled filament, such as those used for si nlighting purposes, the sagging of the ament permits it to incline to the vertical instead of projecting horizontally. Such alterations impair the lamps efliciency, with the consequent early failure of the same.

One of the'cause's for the sagging of the tungsten-coils, when hot, is known to be certain conditions of their crystalline structure. A sag wire is characterized by small crystals slor grains. The principal characteristic of non-sag wire is its large-grain structure. The grains should be largeas to length and cross section. It is also desirable that the crystals have irregular surfaces so that they may interlock and thus form a more stable structure.

- Another form of internal alteration common to metallic filaments is known as oft setting, which consists of a lateral shifting or displacement of one portion of filament with respect to an adjacent portion. It has been proposed tocontrol this structural change by the addition of auxiliary substances which resist off-setting through retardation of grain growth. 'For this purpose thorium oxide is generally used. For a further explanation of this phenomenon reference may be had to United States Pat- Application filed January 13, 1921.

Serial No. 437,035.

ent No. 1,180,264, issued to Anton Lederer, April 18, 1916.

I have discovered that some oxides, par-- ticularly the alkali oxides and the alkali earths, such as lithium oxide, sodium oxide, calcium oxide, etc., when mixed with a compound of tungsten promote grain growth during the process of manufactun ing drawn tungsten, that is, cause the grains or crystals to grow in size rather than retard their growth, as is the case in the particular materials heretofore employed to prevent offsetting. I have also discovered that some of these, such as lithium oxide and sodium oxide, not only cause the crystals to grow in all directions but direct the growth along the axis of the wire so that the crystals are of greater length than width when the filamentary material contains one or more of these ox-. ides. This crystalline structureis valuable because it results in a non-sag wire. Furthermore, lmhave discovered that other oxides, such as potassium oxide, in addition to causing the crystals to grow in sizeand directing their growth along the axis of the wire, cause the crystals to take on irregular surfaces and thus interlock, the value of which has been stated above. 7

It is, therefore an object of my invention to provide a controllable and simplified process for the production'of a non-sag structure in highly-refractory filamentary materials by the addition of suitable metallic oxides, followed by mechanical Workmg.

A special object of the invention is the provision of a process especially applicable to the treatment of tungsten for producing a non-sag structure when the tungsten is drawn into filamentary form.

Although my invention is applicable to producing bodies from refractory metals generally, for the purpose of illustration, I will describe how it may be practiced in producing a tungsten wire possessing nonsag properties developed by the process contemplated by me.

A solution of any soluble salt of the alkali or alkali-earth metals, such as the nition containing .8 of a, gramof potassium oxide (K is added to a kilogram of tungsten trioxide.- This mixture, -,when dried at 300 C. to 700 CL, eonta1ns..08%

'potassiiun oxide. It is then subjected to a gen at as vlow 'a temperature as possible,

mixing the reduced material with an equal weight of tungsten trioxide and reduclng this mixture by passing it through a fur- .nace having a hydrogen atmosphere ata temperature of about 600 C. to 800 C. The resultant powder is compressed to form billets or slu s about-16 inches long and A" square; i, amperes is passed through this slugto effeet a sintering action; at the same time most of the potassium nitrat-eis volatilize as potassium oxide and thus removed from the tungsten slug. The slug is then swaged and drawn into wire according to any approved process for producing drawn tungsten wire.

Fromthe foregoing it is to be appreciated that the additive substance which is incorporated into the base material may vary,

and that the quantity necessary to produce. the desired result may likewise vary. have found that, in certain sizes of filaments, lithium oxide is'to be preferred over other compounds of the alkali or alkaline earth metals, and that, for other sizes of filament, potassium oxide appears to be the most satisfactory. For example, ina tungsten wire of 25 mil diameter,such as is usedm an lncandescentlamp employed as alight source for projection work, hthium oxide It will, therefore,

promotes a crystalline structure which is found to be very non-sa as compared to an untreated or undoped fi lament of'the samediameter. Onthe other hand, potassium oxide has been found to give the best results when used in filaments of 10 ,mil or less m diameter. However, I consider it posslble for a single substance to beeffective.

'in aiding coarse crystallization in all sizes of wire, providing a suitable rocess is employed fo r incorporating t e additional substance into the filamentary material. It

appears to be largely a matter of rendering atent certain characteristics which'are deayed or not..present in the" various stages of the drawingoi': the tungsten or filamentary material into sizes of wire suitable for.

all types of lamps.

be seen that my invention" resides not so much in the quantlty or methodof adding a given substance capable of exercising control over crystal Jgrowth. as it is 'in appreciatingthat the presence of such a substance exerts such a F control WhlCh may be utilized in obtaining ar beneficial result largely desirable in oer-q tam forms of incandescent lamps M crystal structure in .nealed or burned, and reducing by hydrolectric current of about 1600 g What is claimed is: I

'1. The method of preparing tungsten powder from which filamentary material may be produced having. a definite predetermined grain or crystal, structure, which renders the filament resistant to substantial sagging andofi'setting when burned at high temperatures which comprises mixing with a tungsten oxide free from compounds deleteriously vaffecting grain growth, a predetermined quantity of: at least one salt of a particular alkali oralkaline earth metal capable of promoting a definite grain or t e filament when anen. v

2. The methodof preparing tungsten'powder from which filamentary material may be produced having. an interlocking grain or crystal structure, which comprises mix-- ing w1th a tungsten oxide free from com-v pounds deleteriously afl'ecting grain growth, a predetermined quantity of at least one salt of a particular alkali or-alkaline earth metal.

capable of promoting said grainlor crystal structure in the filament when annealed or burned, and reducing by hydrogen.

.3. The method of preparing tungsten fila- I ments having a definite predetermined grain or crystal structure therein vwhen burned or annealed which renders the filament resistant to sagging and offsetting, which com-' .grain or crystal structure in' the filament when burned or v annealed, reducing by means of hydrogen to obtain a mixture of metallic tungsten and a compound 01 the alkali metal employed pressing the powder to form, sinte'ring ing to filament size.

4. The meth'od of preparing tungsten filatal structure therein wherrburned or an- 'nealed, which comprises mixing with tungsten oxide free from com oundsf deleterious- 1y affecting grain growt apredetermined quantity of at least, one salt ofa partlcular ifilament size.

"The method of preparing tungstenv wd'er from which filaments may be prouced having ains or crystals of greater len h than wi th and'which have irregular sur acesinterlocking with adjacent g'ystals,

. which comprises with oxide alkali or alkaline mechanically work- I ments having an-interloclnng grain or cryssmtermg and sintering and moaaaa free from deleterious compounds. afiecting grain growth, apredetermlned quantity of a compound containing potassium or the like, which is capable of. promoting said crystal formation, and reducing by hydrogen.

6. The methodof preparing tungsten filaments having grains or crystals of greater len th than width and having irregular 'sur aces interlocking with adjacent crystals, said structure being developed after burnin with tungsten oxide free from deleterious compounds affecting grain or-crystal growth 15 powder free fr "m compounds inhibiting the formati n of a definite crystal structure and containing a predetermined quantity of a compound containing at least one salt of a particular alkali or alkaline earth metal capable of promoting a definite crystal structure when the powder is fabricated into wire and burned orannealed. I

8. A tungsten base material from which wire may be produced having an interlocking crystal or grain formation, which comor annealing, which comprises mixing prises tungsten powder free from compounds inhibiting the formation of a definite crystal structure and containing a predetermined quantity of a compound containing at least one salt of a particular alkali or alkaline earth metal capable of promoting said crystal structure when the powder is fabricated into wire and burned or annealed.

9. A tungsten base material from which wire may be .produced having grains or crystals of greater length than width and with interlocking contacting surfaces which renders the wire resistant to sagging and offsetting, which comprises tungsten metal free from compounds inhibiting the formation of a definite crystal development but containin a predetermined quantity of a compoun of potassium and the like, capable of promoting said crystal formation when the owde'r is fabricated into wire and burne or annealed.

10. A substantially pure tungsten filament having a definite predetermined grain or crystal formation, said formation having been produced by the addition to tungsten oxide free from compounds inhibiting the formation of a definite grain or crystal structure, of a predetermined quantity of a compound or compounds containing particular alkali or alkaline earth metals selected in accordance with the definite crystal or grain=structure desired. A

In testimony whereof, I have hereunto subscribed my name this twelfth day of January, 1921.

\ WILLIAMB. GERO. 

